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19-1117; Rev 0; 8/96
Low-Cost, Low-Dropout, Dual Linear Regulator
_______________General Description
The MAX8862 low-cost, low-dropout, dual linear voltage regulator is ideal for battery-powered and portable applications. The regulators have independent supply inputs and provide 250mA and 100mA, respectively, with a full-load dropout voltage of 160mV. Both regulators use P-channel MOSFET pass transistors and maintain low quiescent current independent of load current. In dropout, the MOSFET does not suffer from excessive base currents, as do saturated PNP transistors. The MAX8862 output voltage is preset to 4.95V (L), 3.175V (T), or 2.85V (R). This device employs Dual ModeTM operation, allowing user-adjustable outputs from +2V to +11V with external resistors. The input supply-voltage range is 2.5V to 11.5V. Other features include independent shutdown, power-good indicator, short-circuit and reverse-battery protection, and thermal shutdown. The MAX8862's regulators are ideal power supplies for the radio and the microcontroller (C) used in digital, cordless, and PCS phones. The main regulator is optimized for superior transient and dynamic response, while the secondary regulator exhibits low-output, wideband noise. The MAX8862 comes in a 16-pin SO package with a lead frame that uses multiple GND pins as a heat sink for additional thermal dissipation.
____________________________Features
o Low Cost o Guaranteed 250mA and 100mA Output Currents, with Current Limiting o Dual Mode Operation: Fixed or Adjustable Output from +2V to +11V o +2.5V to +11.5V Input Range o 160mV Dropout Voltage at 200mA Output Current o Low Supply Current--Even in Dropout 200A Operating <1A Shutdown o Power-Good Indicator o Reverse-Battery Protection o Thermal Overload Protection
MAX8862
______________Ordering Information
PART* MAX8862_ESE TEMP. RANGE -40C to +85C PIN-PACKAGE 16 Narrow SO
*Insert the desired suffix letter (from the table below) into the blank to complete the part number.
SUFFIX L T R FIXED OUTPUT VOLTAGE (V) 4.95 3.175 2.85
________________________Applications
Cellular Phones PCS Phones Modems Electronic Planners Cordless Phones PCMCIA Cards Hand-Held Instruments
__________________Pin Configuration
TOP VIEW
__________Typical Operating Circuit
INPUT 1 2.5V TO 11.5V 1F OUTPUT 1 AT 250mA 3.3F 100k PWROK1 REF2 0.1F IN1 SHDN1 IN2 SHDN2 1F OUTPUT 2 AT 100mA 2.2F INPUT 2 2.5V TO 11.5V IN1 1 SHDN1 2 PWROK1 3 16 N.C. 15 SET1 14 OUT1
MAX8862
OUT1 OUT2
GND 4 GND 5 OUT2 6 SET2 7 N.C. 8
MAX8862
13 GND 12 GND 11 REF2 10 SHDN2 9 IN2
GND SET1 SET2 GND
Narrow SO
Dual Mode is a trademark of Maxim Integrated Products.
________________________________________________________________ Maxim Integrated Products 1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800
Low-Cost, Low-Dropout, Dual Linear Regulator MAX8862
ABSOLUTE MAXIMUM RATINGS
IN1, IN2 to GND (Note 1).....................................................12V SET1, SHDN1, PWROK1 to GND.............. -0.3V to (VIN1 + 0.3V) SET2, SHDN2, REF2 to GND ....................... -0.3V, (VIN2 + 0.3V) Output Short-Circuit Duration ............................................Infinite Continuous Power Dissipation (TA = +70C) 16-Pin Narrow SO (derate 20mW/C above +70C) ............... 1W Operating Temperature Range ...........................-40C to +85C Junction Temperature .....................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10sec) ............................ +300C
Note 1: Connect SHDN1 to IN1 and SHDN2 to IN2 through 20k resistors to limit current flow in case a battery is reversed.
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS (Notes 2, 3)
(VIN_ = VOUT_(TYP) + 1V, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER Input Voltage Range Output Voltage Output Voltage Range Maximum Output Current Current Limit Quiescent Current Shutdown Supply Current VIN1 = VIN2 = 11.5V IOUT1 = IOUT2 = 1mA IOUT1 = 200mA, MAX8862L/T Dropout Voltage (Note 4) IOUT2 = 100mA, MAX8862L/T IOUT1 = 200mA, MAX8862R IOUT2 = 100mA, MAX8862R IOUT1 = IOUT2 = 15mA Line Regulation VIN2 = (VOUT2 (TYP) + 1V) to 11.5V Load Regulation IOUT1 = 0mA to 250mA, COUT1 = 3.3F IOUT2 = 0mA to 100mA, COUT2 = 2.2F COUT2 = 2.2F ZOUT2 = 10mA COUT2 = 100F ZOUT2 = 10mA REFERENCE REF2 Output Voltage REF2 Line Regulation REF2 Load Regulation 2 CREF2 = 0.1F VIN2 = 2.5V to 11.5V IREF2 = 0A to 10A 1.230 1.250 1 6 1.270 V mV mV 10Hz < f < 100kHz 10Hz < f < 1MHz 10Hz < f < 100kHz 10Hz < f < 1MHz 0.02 0.015 0.02 277 875 211 667 0.08 %/mA VRMS mVRMS VIN1 = (VOUT1 (TYP) + 1V) to 11.5V VIN1 = 2.5V min, VOUT1 = 2V VIN2 = 2.5V min, VOUT2 = 2V IOUT1 IOUT2 0mA < IOUT1 250mA, 0mA < IOUT2 100mA MAX8862L MAX8862T MAX8862R CONDITIONS MIN 2.5 4.80 3.050 2.75 2 250 100 580 250 200 0.01 1.5 160 160 165 180 0.03 330 350 350 400 0.1 %/V mV 330 1 4.95 3.175 2.85 TYP MAX 11.5 5.15 3.300 2.95 11 V mA mA A A V UNITS V
OUT2 Voltage Noise
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Low-Cost, Low-Dropout, Dual Linear Regulator
ELECTRICAL CHARACTERISTICS (Notes 2, 3)
(VIN_ = VOUT_(TYP) + 1V, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER PWROK1 OUTPUT PWROK1 Trip Voltage PWROK1 Hysteresis PWROK1 Leakage Current PWROK1 Low Voltage Falling edge at SET1 Rising edge at SET1 VPWROK1 = 11.5V ISINK = 0.5mA Shutdown mode, VIN_ = VOUT_(TYP) + 1V to 11.5V Active mode, VIN_ = 11.5V V SHDN_ = 11.5V SET_ = OUT_, IOUT1 = IOUT2 = 15mA VSET_ = 1.30V Internal feedback External feedback 250 1.23 1.8 0.01 1 1.175 1.200 15 0.01 25 1 200 0.45 1.225 V mV A mV V V A CONDITIONS MIN TYP MAX UNITS
MAX8862
SHDN
SHDN_ Logic Low SHDN_ Logic High SHDN_ Leakage Current SET_ INPUT SET_ Reference Voltage SET_ Input Bias Current SET_ Threshold THERMAL PROTECTION Thermal Shutdown Temperature Thermal Shutdown Hysteresis
1.25 0.01
1.28 0.1 40
V A mV
160 20
C
ELECTRICAL CHARACTERISTICS (Notes 2, 3)
(VIN_ = VOUT_(TYP) + 1V, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER Input Voltage Range Output Voltage Output Voltage Range Maximum Output Current Current Limit Quiescent Current Shutdown Supply Current VIN1 = VIN2 = 11.5V IOUT1 = IOUT2 = 1mA IOUT1 = 200mA, MAX8862L/T Dropout Voltage (Note 4) IOUT2 = 100mA, MAX8862L/T IOUT1 = 200mA, MAX8862R IOUT2 = 100mA, MAX8862R VIN1 = 2.5V min, VOUT1 = 2V VIN2 = 2.5V min, VOUT2 = 2V IOUT1 IOUT2 0mA < IOUT1 250mA, 0mA < IOUT2 100mA MAX8862L MAX8862T MAX8862R CONDITIONS MIN 2.5 4.80 3.050 2.740 2 250 100 580 250 200 0.01 1.5 160 160 165 180 330 350 350 400 3 mV 330 1 4.95 3.175 2.85 TYP MAX 11.5 5.15 3.300 2.960 11 V mA mA A A V UNITS V
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Low-Cost, Low-Dropout, Dual Linear Regulator MAX8862
ELECTRICAL CHARACTERISTICS (Notes 2, 3) (continued)
(VIN_ = VOUT_(TYP) + 1V, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER CONDITIONS IOUT1 = IOUT2 = 15mA Line Regulation VIN2 = (VOUT2 (TYP) + 1V) to 11.5V Load Regulation IOUT1 = 0 to 250mA, COUT1 = 3.3F COUT2 = 2.2F, 10Hz < f < 1MHz, IOUT2 = 10mA C = 2.2F, ZOUT2 = 10mA OUT2 Voltage Noise C = 100F, ZOUT2 = 10mA REFERENCE REF2 Output Voltage REF2 Line Regulation REF2 Load Regulation PWROK1 OUTPUT PWROK1 Trip Voltage PWROK1 Hysteresis PWROK1 Leakage Current PWROK1 Low Voltage Falling edge at SET1 Rising edge at SET1 VPWROK1 = 11.5V ISINK = 0.5mA Shutdown mode, VIN_ = VOUT_(TYP) + 1V to 11.5V Active mode, VIN_ = 11.5V V SHDN_ = 11.5V SET_ = OUT_, IOUT1 = IOUT2 = 15mA VSET_ = 1.30V Internal feedback External feedback 250 160 10 1.220 2.0 0.02 1.250 0.01 1 1.290 0.1 30 1.165 1.200 15 0.01 25 1 200 0.45 1.235 V mV A mV V V A V A mV CREF2 = 0.1F VIN2 = 2.5V to 11.5V IREF2 = 0A to 10A 1.217 1.250 1 6 1.277 V mV mV 10Hz < f < 100kHz 10Hz < f < 1MHz 10Hz < f < 100kHz 10Hz < f < 1MHz 0.02 0.015 0.02 277 875 211 667 VRMS 0.10 %/mA VIN1 = (VOUT1 (TYP) + 1V) to 11.5V MIN TYP 0.03 MAX 0.12 %/V UNITS
SHDN
SHDN_ Logic Low SHDN_ Logic High SHDN_ Leakage Current SET_ INPUT SET_ Reference Voltage SET_ Input Bias Current SET_ Threshold THERMAL PROTECTION Thermal Shutdown Temperature Thermal Shutdown Hysteresis
C
Note 2: Guaranteed by design for TA = -40C. Note 3: Guaranteed for a junction temperature (TJ) equal to the operating temperature range. E-grade parts are guaranteed by design to operate up to TJ = +125C. For TJ above +125C, specifications exceed the operating limits. Note 4: Dropout voltage is (VIN_ - VOUT_) when VOUT_ falls to 100mV below its nominal value at VIN_ = (VOUT_ + 1V). For example, the MAX8862 is tested by measuring the VOUT_ at (VIN_ = 5.95V for the MAX8862L, VIN_ = 4.175V for the MAX8862T, and VIN_ = 3.85V for the MAX8862R) then VIN_ is lowered until VOUT_ falls 100mV below the measured value.
4
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Low-Cost, Low-Dropout, Dual Linear Regulator
__________________________________________Typical Operating Characteristics
(VIN1 = VIN2 = 5.3V, CIN1 = CIN2 = 1F, COUT1 = 3.3F, COUT2 = 2.2F, SHDN1 = IN1, SHDN2 = IN2. TA = +25C, unless otherwise noted.)
QUIESCENT CURRENT vs. TEMPERATURE
MAX8862 TOC02
MAX8862
QUIESCENT CURRENT vs. LOAD CURRENT
MAX8862 TOC03
SHUTDOWN CURRENT vs. TEMPERATURE
MAX8862 TOC01
260 240 QUIESCENT CURRENT (A) 220 200 180 160 140 120 100 -40 -20 0 40 60 20 TEMPERATURE (C) 80 VIN1 = VIN2 = 7V VIN1 = VIN2 = 12V
120
120 100 80 VIN1 = VIN2 = 12V 60 40 20 VIN1 = VIN2 = 7V 0 -40
QUIESCENT CURRENT (A)
110 IQ2 100 IQ1 90
100
80 0.001 0.01
10 1 0.1 LOAD CURRENT (mA)
SHUTDOWN CURRENT (nA)
100
1000
-20
0
20
40
60
80
100
TEMPERATURE (C)
OUTPUT VOLTAGE vs. TEMPERATURE
MAX8862TOC06
OUTPUT VOLTAGE vs. LOAD CURRENT
NORMALIZED OUTPUT VOLTAGE (%)
MAX8862TOC04
MAX8862T OUTPUT VOLTAGE & QUIESCENT CURRENT vs. SUPPLY VOLTAGE
MAX8862TOC05
3.27 3.26 OUTPUT VOLTAGE (V) 3.25 3.24 OUT2 3.23 3.22 3.21 3.20 -40 -20 40 60 TEMPERATURE (C) 0 20 80 OUT1
101 100 VOUT1 99 98 97 96 95 0.001 VOUT2
4 VOUT1/VOUT2 OUTPUT VOLTAGE (V) 3
260 240 220 200 QUIESCENT CURRENT (A)
2
(IQ1 + IQ2)
180 160
1
140 120
0 0.01 10 1 0.1 LOAD CURRENT (mA) 100 1000 2 3 4 6 7 8 9 10 11 SUPPLY VOLTAGE (V) 5 12
100
100
DROPOUT VOLTAGE vs. LOAD CURRENT
525 DROPOUT VOLTAGE (mV) 450 OUT2 375 300 225 OUT1 150 75 0 0 40 80 120 160 200 240 280 320
MAX8862TOC07
OVERSHOOT AND TIME EXITING SHUTDOWN MODE
MAX8862TOC14
600
1V/div A 0V
1V/div
B 0V 20s/div VIN1 = 5.3V, IOUT1 = 5mA A = SHDN1, 0.8V TO 2.4V, 1V/div B = OUT1, 1V/div
LOAD CURRENT (mA)
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5
Low-Cost, Low-Dropout, Dual Linear Regulator MAX8862
____________________________Typical Operating Characteristics (continued)
(VIN1 = VIN2 = 5.3V, CIN1 = CIN2 = 1F, COUT1 = 3.3F, COUT2 = 2.2F, SHDN1 = IN1, SHDN2 = IN2. TA = +25C, unless otherwise noted.)
OUT1 NOISE AND RIPPLE
MAX8862TOC08
OUT2 NOISE AND RIPPLE
MAX8862TOC09
VOUT 1mV/div
VOUT 500V/div
5s/div IOUT1 = 250mA, AC COUPLED
5s/div IOUT2 = 100mA, AC COUPLED
OUT1 LOAD-TRANSIENT RESPONSE
MAX8862TOC10
OUT2 LOAD-TRANSIENT RESPONSE
MAX8862TOC11
300mA A 200mA
0mA
A
0mA
B B 50mV/div 50mV/div
2ms/div VIN1 = 7V, VOUT1 = 3.2V A = LOAD CURRENT, 0mA TO 300mA, 0.2A/div B = VOUT1 RIPPLE, 50mV/div, AC COUPLED
2ms/div VIN2 = 7V, VOUT2 = 3.2V A = LOAD CURRENT, 0mA TO 200mA, 0.2A/div B = VOUT2 RIPPLE, 50mV/div, AC COUPLED
OUT2 LINE-TRANSIENT RESPONSE
MAX8862TOC12
OUT1 LINE-TRANSIENT RESPONSE
MAX8862TOC13
6.5V A A 5.5V
6.5V 5.5V
B
50mV/div
B
50mV/div
1ms/div IOUT2 = 200mA, VOUT2 = 3.2V A = VIN2, 5.5V TO 6.5V, 1V/div B = VOUT2 RIPPLE, 50mV/div, AC COUPLED
1ms/div IOUT1 = 300mA, VOUT1 = 3.2V A = VIN1 = 5.5V TO 6.5V, 1V/div B = VOUT1 RIPPLE, 50mV/div, AC COUPLED
6
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Low-Cost, Low-Dropout, Dual Linear Regulator
______________________________________________________________Pin Description
PIN 1 2 3 4, 5, 12, 13 6 7 8, 16 9 10 11 14 15 NAME IN1 SHDN1 PWROK1 GND OUT2 SET2 N.C. IN2 SHDN2 REF2 OUT1 SET1 FUNCTION Main Regulator Supply Input (2.5V to 11.5V). Bypass with a 1F, low-ESR capacitor to GND. Main Regulator Shutdown Input. A logic low turns off the main regulator and power-good comparator. Power-Good Output. This open-drain output is low when VOUT1 is out of regulation (VOUT1 is 4% lower than its nominal value). Ground. Connect to a ground plane to maximize thermal dissipation. Secondary Regulator Output. Bypass with a 2.2F low-ESR (< 0.5) capacitor to GND. To improve load-transient response and noise performance, use a higher-value, lower-ESR capacitor. OUT2 Voltage-Set Input. Connect to GND for the factory-preset output voltage. Connect to a resistive divider from OUT2 to GND for adjustable output voltage. No connect. There is no internal connection to this pin. Secondary Regulator Supply Input (2.5V to 11.5V). Bypass with a 1F, low-ESR capacitor to GND. Secondary Regulator Shutdown Input. A logic-low input turns off the secondary regulator and the reference. Secondary Reference Output. Bypass with a 0.1F capacitor to GND. Main Regulator Output. Bypass with a 3.3F, low-ESR (< 0.5) capacitor to GND. To improve loadtransient response and noise performance, use a higher-value, lower-ESR capacitor. OUT1 Voltage Set Input. Connect to GND for the factory-preset output voltage. Connect to a resistive divider from OUT1 to GND for adjustable output voltage.
MAX8862
_______________Detailed Description
The MAX8862 features Dual ModeTM operation, allowing a fixed output of 4.95V (L), 3.175V (T), or 2.85V (R), or an adjustable output from 2V to 11V. The regulator's outputs, OUT1 and OUT2, supply 250mA and 100mA, respectively. The block diagram (Figure 1) shows the contents of each regulator. Note that the main regulator provides a power-good indicator, and the secondary regulator's reference output voltage is available at REF2. The 1.25V bandgap reference is connected to the error amplifier's inverting input. The error amplifier compares this reference with the selected feedback voltage and amplifies the difference. The MOSFET driver reads the error signal and applies the appropriate drive to the P-channel transistor. If the feedback voltage is lower than the reference, the pass transistor's gate is pulled lower, allowing more current to pass and increase the output voltage. If the feedback voltage is too high, the pass transistor's gate is pulled up, allowing less current to pass to the output.
The output voltage is fed back through either an internal resistor voltage divider connected to OUT1/ OUT2, or an external resistor network connected to SET1/SET2. The Dual Mode comparator examines VSET1/VSET2 and selects the feedback path. If this voltage is below 40mV, internal feedback is used and the output voltage is regulated to the factory-preset voltage.
Internal P-Channel Pass Transistor
The MAX8862's P-channel pass transistor provides several advantages over similar designs using PNP pass transistors, including longer battery life. The P-channel MOSFET requires no continuous base current, thereby reducing quiescent current considerably. PNP regulators normally waste a considerable amount of current in dropout when the pass transistor saturates; they also use high base-drive currents under large loads. The MAX8862 does not suffer from these problems: it consumes only 200A of quiescent current for both regulators under light and heavy loads, as well as in dropout.
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7
Low-Cost, Low-Dropout, Dual Linear Regulator MAX8862
1N1 R1
OUT1
PWROK1 SHDN1 BIAS 50mV
G1 SET1 1.25V R2 80mV GND IN2 R3 OUT GND
MAX8862
SHDN2 BIAS
REF2
G1
SET2
1.25V R4
GND
80mV
GND
Figure 1. Functional Diagram
Output Voltage Selection
The MAX8862's Dual Mode operation allows a fixed or adjustable output voltage. In preset/internal-feedback mode (SET1/SET2 = GND), output voltages are factory preset to 4.95V (L), 3.175V (T), or 2.85V (R). In adjustable/external feedback mode, output voltage is adjusted between 2V and 11V with two external resistors connected as a voltage divider to SET1/SET2 (Figure 2). Since the input bias current at SET1/SET2 is <0.1A, large resistance values can be used for R1 and R2 to minimize power consumption without losing accuracy. Select R2 in the 10k to 400k range. R1 is given by: R1 = R2 (VOUT / VSET - 1) where VSET = 1.25V.
8
Power-Good Comparator
The MAX8862's main regulator features a power-good indicator that asserts when the output voltage falls out of regulation. In internal-feedback mode, the opendrain PWROK1 output goes low when OUT1 falls 4% below its nominal value. When used in external feedback mode, PWROK1 goes low when VSET1 falls below 1.2V. A 100k pull-up resistor from PWROK1 to VIN1 provides a logic-control signal. This resistor also minimizes current flow to the input in case the battery is reversed. PWROK1 can be used to reset a microcontroller or to drive an external LED for indicating a power failure.
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Low-Cost, Low-Dropout, Dual Linear Regulator
Thermal Overload Protection
Thermal overload protection limits the MAX8862's total power dissipation. When the junction temperature exceeds TJ = +160C, the thermal sensor sends a signal to the shutdown logic, turning off the pass transistors and allowing the device to cool down. The thermal sensor turns the pass transistors on again after the IC's junction temperature decreases by 20C. If the thermal overload condition persists, OUT1 and OUT2 pulse on and off. Thermal overload protection is designed to protect the MAX8862 during fault conditions. For continuous operation, the absolute maximum junction temperature rating of TJ = +150C should not be exceeded.
MAX8862
MAX8862
OUT_ R1 SET_ R2
OUTPUT
GND
Reverse-Battery Protection
Figure 2. Adjustable Output Voltage
Reference
The MAX8862 provides a precision 1.25V reference at REF2. Bypass REF2 with a 0.1F capacitor to ground. Larger bypassing capacitors will further reduce the secondary regulator's wideband noise.
Shutdown
The MAX8862's regulators have individual shutdown controls. A logic low on either SHDN1 or SHDN2 turns off the corresponding internal reference, error comparator, and pass transistors' control logic, reducing quiescent current to less than 1A.
This feature protects the MAX8862 against polarity reversal at the supply inputs. The inputs can handle negative voltages up to -12V without suffering any ill effects. When the input polarity is reversed, the output will be at the same potential as ground, and no current will flow from the output back to the input. This feature protects both the device and the supply-voltage source. The reverse currents that flow back to the input are due to RPWROK1 , RSHDN1, and RSHDN2. These currents are approximately: IREV1 = |VIN1| / (RSHDN1 + RPWROK1) and IREV2 = |VIN2| / RSHDN2. When operating the MAX8862 in continuous mode (VSHDN1 = VIN1 and VSHDN2 = VIN2) place a resistor (>20k) between shutdown and supply inputs to limit the current flow in case the battery is reversed.
Current Limiting
The MAX8862 features a current limit for each regulator. It monitors and controls the pass transistor's gate voltage, limiting the output current to 580mA for the main regulator and 250mA for the secondary regulator. The current limits apply to all input and output voltage conditions. The outputs can be shorted to ground for an indefinite period of time if the package can dissipate (VIN1 x ILIM1 + VIN2 x ILIM2) without exceeding TJ = +150C (see the Power Dissipation and Operating Region section).
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9
Low-Cost, Low-Dropout, Dual Linear Regulator
pins to ground using a large pad or ground plane. Where this is impossible, place a copper plane on an adjacent layer. For a given power dissipation, the pad should exceed the associated dimensions in Figure 3. This figure shows a typical thermal resistance for a 35m-thick copper foil as a function of its area1. The power dissipation across the device is given by: P = IOUT1 (VIN1 - VOUT1) + IOUT2 (VIN2 - VOUT2). The resulting power dissipation is as follows: P = (TJ - TA) / (JB + BA) where (TJ - TA) is the temperature difference between the MAX8862 die junction and the surrounding air, JB (or JC) is the thermal resistance of the package, and BA is the thermal resistance through the printed circuit board, copper traces, and other materials to the surrounding air. The MAX8862's narrow SO package has a thermal resistance of JB = +50C/W. The MAX8862 regulators deliver the rated output currents and operate with input voltages up to 11.5V, but not simultaneously. High output currents can only be sustained when input-output differential voltages are small, as shown in Figure 4.
MAX8862
80 R0BA(C/W)
60
40
20
0 0 5 10 15 20 25 30 35 PC-BOARD COPPER FOIL AREA (Cm2)
Figure 3. Typical Copper Thermal Resistance vs. Copper Ground Pad Area
400 MAXIMUM CURRENT MAXIMUM OUTPUT CURRENT (mA) (IOUT1 + IOUT2) 350 300 250 200 150 100 50 0 2 3 4 5 6 7 8 9 10 11 12 SUPPLY VOLTAGE (V) OPERATING REGION AT TA = +25C, TJ = +125C (R) (T) (L) (R) MAXIMUM SUPPLY VOLTAGE (T) (L)
MAX8862 FIG03 MAX8862FGIG04
100
Capacitor Selection and Regulator Stability
Filter capacitors are required at the MAX8862's inputs and outputs. 1F ceramic capacitors are required at the inputs. The minimum output capacitance required for stability is 3.3F for OUT1 and 2.2F for OUT2. The capacitor values depend primarily on the desired power-up time and load-transient response. Loadtransient response is improved by using larger capacitor values. Input and output filter capacitors should be soldered directly to pins to minimize lead inductance of PC board traces. The output capacitor's equivalent series resistance (ESR) affects stability and output noise. Surface-mount ceramic capacitors have a very low ESR and are available up to 10F. Otherwise, other low-ESR (<0.5) capacitors should be used. If the selected capacitor's ESR is higher than the recommended value, the capacitor value should be increased proportionally to maintain minimum output noise under all input voltage and output load conditions. Paralleling two or more capacitors also results in lower ESR.
Figure 4. Safe Operating Regions: Main and Secondary Regulators Maximum Output Current vs. Supply Voltage
__________Applications Information
Power Dissipation and Operating Region
The MAX8862's maximum power dissipation depends on the thermal resistance of the case and circuit board, the temperature difference between the die junction and ambient air, and the rate of air flow. The GND pins of the MAX8862 SO package perform the dual function of providing an electrical connection to ground and channeling heat away. Connect all GND
1This
graph was generated by Mr. Kieran O'Malley of Cherry Semiconductor Corp. and was published in the October 26, 1995, issue of EDN magazine. 10 ______________________________________________________________________________________
Low-Cost, Low-Dropout, Dual Linear Regulator MAX8862
MAX8862FIG05A
70 OUT1 VIN1 = 1Vp-p CIN1 = 1F COUT1 = 3.3F
65 60 55 PSRR (dB) 50 45 40 35 B A
60 PSRR (dB)
50
A B C
OUT1 VIN1 = 1Vp-p CIN1 = 1F IOUT1 = 100mA
40
30
A: IOUT1 = 1mA B: IOUT1 = 10mA C: IOUT1 = 100mA 0.01 0.1 1 FREQUENCY (kHz) 10 100
30 25 20 A: COUT1 = 100F B: COUT1 = 10F 0.1 1 10 100 1000
20
FREQUENCY (kHz)
Figure 5a. Power-Supply Rejection Ratio vs. Ripple Frequency for Light and Heavy Loads
Figure 5b. Power-Supply Rejection Ratio vs. Ripple Frequency for Various Output Capacitors
Noise
The MAX8862's OUT1 exhibits about 2.5mVp-p, and OUT2 exhibits 1mVp-p of noise under full-load conditions. When using the MAX8862 for applications that include analog-to-digital converters (ADCs) with resolutions greater than 12 bits, consider the ADC's powersupply-rejection specifications.
Overshoot and Transient Considerations
The Typical Operating Characteristics section shows power-up, line, and load-transient response graphs. Typical transients for step changes in the load current from 0mA to 300mA are 100mVp-p. During recovery from shutdown, overshoot is minimized by the 1F input, and output capacitors (3.3F for OUT1, and 2.2F for OUT2).
PSRR and Operation from Sources Other than Batteries
The MAX8862 is designed to achieve low dropout voltages and low quiescent currents in battery-powered systems. However, to gain these benefits; the device must trade away power-supply noise rejection, as well as swift response to supply variations and load transients. For a 1mA load current, power-supply rejection typically changes from 58dB to 43dB when the input frequency is changed from 1Hz to 10kHz. At higher frequencies, the circuit depends primarily on the output capacitor's characteristics, and the PSRR increases (Figure 5). When operating from sources other than batteries, supply-noise rejection and transient response can be improved by increasing the value of the input and output capacitors and employing passive filtering techniques. Do not use power supplies with ripple voltages exceeding 200mV at 100kHz.
Input-Output (Dropout) Voltage
A regulator's minimum input-to-output voltage differential (or dropout voltage) determines the lowest usable supply voltage. In battery-powered systems, this determines the useful end-of-life battery voltage. Since P-channel MOSFETs are used as pass transistors, the dropout voltage is the product of the RDS(ON) and the load current (see the Electrical Characteristics).
___________________Chip Information
TRANSISTOR COUNT: 457
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MAX8862FIG05B
70
11
Low-Cost, Low-Dropout, Dual Linear Regulator MAX8862
________________________________________________________Package Information
DIM INCHES MAX MIN 0.069 0.053 0.010 0.004 0.019 0.014 0.010 0.007 0.157 0.150 0.050 0.244 0.228 0.050 0.016 MILLIMETERS MIN MAX 1.35 1.75 0.10 0.25 0.35 0.49 0.19 0.25 3.80 4.00 1.27 5.80 6.20 0.40 1.27
D A e B
0.101mm 0.004in.
0-8
A1
C
L
A A1 B C E e H L
E
H
Narrow SO SMALL-OUTLINE PACKAGE (0.150 in.)
DIM PINS D D D 8 14 16
INCHES MILLIMETERS MIN MAX MIN MAX 0.189 0.197 4.80 5.00 0.337 0.344 8.55 8.75 0.386 0.394 9.80 10.00
21-0041A
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
12 __________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600 (c) 1996 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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